Method of determining end of cleaning of semiconductor manufacturing apparatus

ABSTRACT

In a method for determining an end of cleaning of a semiconductor manufacturing apparatus according to the invention, when the interior of a semiconductor substrate process chamber of the semiconductor manufacturing apparatus is cleaned by dry etching using plasma discharge, a constant current or voltage is supplied from a high-frequency power source to discharge electrodes during plasma discharge, an impedance between the electrodes or a temperature in the process chamber is monitored, a time point at which the impedance or temperature is abruptly changed is detected, and this time point of detection is determined to be an end of cleaning.

TECHNICAL FIELD

The present invention relates to a method of determining an end ofcleaning of a semiconductor manufacturing apparatus, which is adapted todetermine an end of cleaning when the interior of a semiconductorsubstrate process chamber of a semiconductor manufacturing apparatus iscleaned by dry etching using plasma discharge.

BACKGROUND ART

Mass spectrometry, emission spectroscopy, and the like are known asmethods of monitoring and end of cleaning when the interior of areaction chamber (deposition chamber) of a plasma CVD (chemical vapordeposition) apparatus is cleaned by dry etching using plasma discharge.In addition, Japanese Patent Disclosure (Kokai) No. 61-145825 disclosesa power measurement method of detecting an end of cleaning by measuringa reflecting power of a plasma discharge power or a bias voltagegenerated by a plasma electrode. According to a known time controlmethod, a time for dry etching cleaning is controlled by estimating thetotal thickness of a film deposited in a reaction chamber from thethickness of a film deposited on a semiconductor substrate andcalculating a cleaning time in accordance with the estimated total filmthickness.

In the power measurement method, however, since the inductance andcapacitance of a matching circuit inserted between a high-frequencypower source and a discharge electrode is fixed at the start ofcleaning, the inductance may be set in a mismatched state by the end ofcleaning, and hence a plasma state becomes unstable. This worsensreproducibility of a cleaning process under the same conditions, and asa result, the time required for cleaning becomes long.

In the time control method, a deposition film thickness in the reactionchamber cannot be accurately measured, and overetching must be performedfor a period of time longer than a calculated time by 40% or more inconsideration of a variation in estimated total film thickness. For thisreason, the operation efficiency of a plasma CVD apparatus is degraded,and the throughput of semiconductor substrates is decreased. Inaddition, since a carbon contamination layer is formed on an electrodesurface during the long overetching operation described above because ofthe use of an etching gas (normally, a CF₄ /O₂ gas), the state of thereaction chamber becomes unstable. For this reason, in order to obtainuniformity within ±5% of the thickness of a plasma CVD film on asemiconductor substrate, a deposition process must be frequentlyperformed on a dummy substrate to stabilize the state of the reactionchamber. This operation further decreases the operation efficiency andthe throughput.

PROBLEMS TO BE SOLVED BY THE INVENTION

As described above, in the power measurement method, the problems areassociated with the fact that the impedance is mismatched duringcleaning. The problems posed in the time control method are associatedwith the fact that the operation efficiency of the semiconductormanufacturing apparatus is decreased. The present invention has beenmade in consideration of the above situation, and has as its object toprovide a method of determining an end of cleaning of a semiconductormanufacturing apparatus, in which an end of cleaning can be determinedwith high precision in a real time manner, and the operation efficiencyof the semiconductor manufacturing apparatus can be increased byshortening the time required for cleaning.

MEANS FOR SOLVING THE PROBLEMS

According to the present invention, a method of determining an end ofcleaning of a semiconductor manufacturing apparatus is characterized inthat when the interior of a semiconductor substrate process chamber ofthe semiconductor manufacturing apparatus is cleaned by dry etchingusing plasma discharge, an impedance between discharge electrodes or atemperature in the semiconductor substrate process chamber is monitoredwhile a constant current or voltage is supplied from a high-frequencypower source to the discharge electrodes during plasma discharge anabrupt change in the impedance or temperature is detected, which isdetermined to be an end of cleaning.

FUNCTION

It has been confirmed that an abrupt change point of an impedancebetween the electrodes during cleaning or a temperature in the processchamber is an end of cleaning. The impedance or the temperature can bemonitored with high precision during cleaning in a real time manner.Therefore, an end of cleaning can be determined with high precision, andthe operation efficiency of the semiconductor manufacturing apparatuscan be improved. In addition, since a stable plasma state can beobtained by supplying a constant current or voltage to the dischargeelectrodes during cleaning, the reproducibility of cleaning under thesame conditions can be improved. As a result, the time required forcleaning can be shortened.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing an arrangement of a plasma CVD apparatus of aparallel plate electrode type to which a method of determining an end ofcleaning of a semiconductor manufacturing apparatus according to anembodiment of the present invention is applied;

FIG. 2 is a graph showing a relationship between the cleaning time, thevoltage between electrodes, and an injected electrode current in theapparatus of FIG. 1;

FIG. 3 is a graph showing the relationship between the number ofcleaning operations and the thickness of film deposited on a dummysubstrate by dummy deposition in a batch process when the method of thepresent invention is employed;

FIG. 4 is a view showing an arrangement of a plasma CVD apparatus towhich a method according to another embodiment of the present inventionis applied; and

FIG. 5 is a graph showing the relationship between the cleaning time andtemperature in the chamber of the apparatus of FIG. 4.

BEST MODE OF CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail withreference to the accompanying drawings.

In a plasma CVD apparatus of a parallel plate electrode type shown inFIG. 1, reference numeral 1 denotes a reaction chamber; 2, an upperelectrode; 3, a lower electrode; 4, a table on which a semiconductorsubstrate is mounted; 5, a reactive gas (e.g., CF₄ +O₂) feed path; 6, anexhaust port; 7, a load lock chamber; 8, a semiconductor substrateconveyor system; 9, an inactive gas (e.g., N₂) feed path; and 10, aheater which is incorporated in the apparatus to heat uppper electrode2. Outside of chamber 1, the apparatus comprises heater power source 11for energizing the heater, driving system 12 for rotating lowerelectrode 3, a reaction chamber exhaust system 13, load lock exhaustsystem 14, high-frequency power source 15 for generating ahigh-frequency power of, e.g., about 400 kHz, coupling capacitor 16 forsupplying/coupling the high-frequency power to upper electrode 2,current detecting pickup 17 for detecting a current supplied fromhigh-frequency power source 15 to upper electrode 2, voltage detectingpickup 18 for detecting a voltage between upper electrode 2 and lowerelectrode 3 (grounded), measurement control system 19 for measuring animpedance between upper and lower electrodes 2 and 3 on the basis of adetection output from pickup 17, CPU (central processing unit) 20 whichis operated in accordance with a program so as to output an operationstop control signal to high-frequency power source 15 by determining anend of cleaning on the basis of a measurement result from measurementcontrol system 19, and various gas supply sources (not shown).

High-frequency power source 15 incorporates a constant current controlfunction for setting output currents to be constant. Reference symbol Adenotes a CVD film to be cleaned, which is deposited on upper and lowerelectrodes 2 and 3, and side walls in reaction chamber 1 when a plasmaCVD film (e.g., a silicon oxide film and a silicon nitride film) isdeposited on a semiconductor substrate. When film A is deposited to athickness of, e.g., 10 to 20 μm, film A must be removed to preventgeneration of particles.

A method of performing cleaning in reaction chamber 1 by dry etchingusing plasma discharge in a state wherein a semiconductor substrate isremoved from chamber 1 after a batch process of plasma CVD is performedseveral times in the above plasma CVD apparatus will be described below.While reaction chamber 1 is set at a predetermined high temperature andis decompressed, a reactive gas is fed into the chamber, and ahigh-frequency power is supplied to cause plasma discharge. A constantcurrent is kept supplied from high-frequency power source 15 during thisplasma discharge, and the impedance of power source 15 is kept matchedwith an impedance between the electrodes. The injected current suppliedfrom power source 15 is detected by current detecting pickup 17, thevoltage between th electrodes is detected by voltage detecting pickup18, and the impedance between the electrodes is detected by measurementcontrol system 19.

FIG. 2 shows an example of data which is obtained by actually measuringan injected current (constant current) and a voltage between theelectrodes as a function of cleaning time from when the power source isturned on to start the plasma discharge. It is apparent from FIG. 2 thatthe voltage between the electrodes gradually decreases as the cleaningtime elapses, drops abruptly from a certain time point (Q), andgradually decreases again from a certain time point (P).

In this case, when the above process was checked by also utilizing aknown plasma emission spectrum analysis, or a sample semiconductor chipwas arranged in reaction chamber 1 and an etched-off state of the CVDfilm on the chip surface was observed by using an microscope, it wasfound that the cleaning was completed at second time point P at whichthe voltage abruptly changed.

Since the injected current is constant, the impedance between theelectrodes changes in the same manner as the voltage between theelectrodes. Therefore, the second abrupt change point of the impedance Pcan be determined to be an end point of cleaning.

CPU 20 receives the measurement result from measurement control system19, measures an elapsed time from the start time point of dry cleaning(time 0 in FIG. 2), determines the cleaning end point (P), and sets anovertime point (R) of, e.g., 20% of the measured time. CPU 20 performs acontrol function so as to stop an operation of high-frequency powersource 15 when the overtime has elasped. Note that differential voltagevalue |dv/dt| abruptly increases at point Q and abruptly decreases atpoint P in FIG. 2. The contents of a timer counter (not shown) arelatched at the time point when value |dv/dt| is abruptly decreased, anda value 1.2 times the latched contents can be detected as point R.

Examples of etching conditions during cleaning in a practical case areas follows: the reaction gas ratio of CF₄ to O₂ is 9:1; flow rates ofthe gases are 450 and 50 SCCM, respectively; the chamber pressure is0.25 Torr; the chamber temperature is 300° C., and the plasma supplycurrent is 4.0 A (constant).

According to the method of determining an end of cleaning in the aboveembodiment, since an injected current from the power source is keptconstant during cleaning, and the power source impedance is not fixed,and can be matched with the impedance between the electrodes, the plasmastate can be stabilized. Therefore, in comparsion with the conventionalpower measurement method, the variation in time required for cleaningunder the same conditions can be reduced, and hence the required timecan be shortened.

In addition, a change in impedance between the electrodes duringcleaning is monitored in a real time manner, an abrupt change point ofthe impedance is detected, and the detection time point is determined tobe an end of cleaning. Therefore, an end of cleaning can be determinedwith high precision. The operating efficiency of the plasma CVDapparatus can be improved and the throughput is increased as comparedwith the conventional time control method. An increase in throughputwill be described in detail. As described above, since an end ofcleaning can be accurately determined, the amount of overetching can bereduced to be as little as about 20%. For example, assume a timerequired to reach an end of cleaning is 700 minutes. In the conventionaltime control method, if an overetching time is set to 40% of therequired time, 700 minutes×0.4=280 minutes are required. In the aboveembodiment, however, if an overetching time is set to 20% of therequired time, 700 minutes×0.2=140 minutes are required, and hence acleaning time including the overetching time is reduced by 15%. Inaddition, since the overetching time is short, formation of a carboncontamination layer on the electrode surface, due to CF₄ gas being usedduring cleaning, can be suppressed significantly to a small, and thestate of the reaction chamber is relatively free from instability.Consequently, when, for example, dry cleaning is performed every 15times a batch process for depositing a plasma silicon oxide film to athickness of 1.0 μm upon formation of a 1.0-μm thick pre-deposition filmis performed, and decomposition cleaning of the interior of the reactionchamber is performed every five times this dry cleaning is performed,the number of deposition processes (dummy deposition) on a dummysubstrate, which are performed to obtain uniformity within ±5% of thethickness of the plasma silicon oxide film by stabilizing a state in thereaction chamber, can be decreased. That is, as shown in FIG. 3, unlikein the conventional time control method wherein dummy deposition must beperformed after each dry cleaning from the first one, in the aboveembodiment, it is confirmed that dummy deposition is required to deposita dummy deposition film to 3.0 μm only once after the fourth drycleaning. It is apparent from this point that the throughput in theabove embodiment can be increased as compared with the time controlmethod.

In the above embodiment, the plasma CVD apparatus of the parallel plateelectrode type is exemplified. When a tube type plasma CVD apparatushaving a floating electrode is used, a current and a voltage which areintermittently applied are constant. In this case, plasma is generallycontrolled by a current application time so that an end of cleaning canbe determined on the basis of an impedance change characteristic in thesame manner as in the above embodiment by monitoring a relationshipbetween an applied voltage and time integral current.

In addition, in the above embodiment, changes in impedance between theelectrodes during cleaning due to plasma discharge are monitored.Instead of this, changes in the reaction chamber during cleaning may bemonitored to determine an end of cleaning. For this purpose, as shown ina plasma CVD apparatus in FIG. 4, temperature sensor 41 such as athermocouple is arranged near lower electrode 3, and an output fromtemperature sensor 41 when plasma discharge is performed by supplying aconstant current under the same conditions as in the embodiment of FIG.1 is measured by measurement control system 42. Then, CPU 43 receivesthis measurement result, determines a cleaning end point (P), and stopsan operation of high-frequency power source 15 after a predeterminedoveretching operation.

Note that the same reference numerals in FIG. 4 denote the same parts asin FIG. 1. Temperature sensor 41 preferably has a small heat capacity,and may be arranged on a portion of an electrode, a portion of the innerwall of the reaction chamber, or another portion to which an etched filmis or is not adhered.

FIG. 5 shows an example of data obtained by actually measuring thetemperature in the reaction chamber as a function of dry cleaning time.It is apparent from FIG. 5 that the temperature in the chamber rises asthe cleaning time elapses, and drops abruptly at given time point P.

In this case, when this process was checked by a known plasma emissionspectrum analysis or an etched-off state of a sample chip was observed,it was found that the cleaning process ended at point P at which thetemperature reached a maximum value. However, point P at which themaximum value appears (an elapsed time from the start of cleaning) maydeviate slightly from an actual end of etching because conduction anddiffusion conditions of the heat in the reaction chamber vary dependingon the states of plasma and reactive gas flow, and the shape of thechamber. In this case, if a program for causing CPU 43 to receive ameasurement result while counting an elapsed time from the start ofcleaning by using a timer or the like; determine cleaning end point P toset an overetching time of 10% or more (e.g., 20%) of the elapsed timeat this point; and stop an operation of high-frequency power source 15after the overetching time has elasped is loaded in CPU 43, the sameeffects as in the above embodiment can be obtained.

Note that the temperature in the chamber may take a minimum value atcleaning end point P depending on etching conditions and the type offilm to be etched. In this case, an end point may be determined bydetecting an abrupt change in temperature when the minimum valueappears.

In addition, in each embodiment, a cleaning process in the plasma CVDapparatus is described. However, the present invention can be applied toother semiconductor manufacturing apparatuses (e.g., a low-pressure CVDapparatus and an oxide film sputtering apparatus) in which cleaning isperformed by plasma discharge.

Moreover, in the above embodiments, a case wherein plasma discharge iscaused by supplying a constant current from the high-frequency powersource to the discharge electrode is described. However, the presentinvention can be applied to a case wherein plasma discharge is caused byapplying a constant voltage in place of a constant current.

Effects of the Invention

As has been described above, according to the method of determining anend of cleaning of a semiconductor manufacturing apparatus of thepresent invention, an end of cleaning can be determined with highprecision in a real time manner, and hence the time required forcleaning can be shortened, the operation efficiency of the semiconductormanufacturing apparatus can be improved, and other effects can beobtained.

We claim:
 1. An improved method of determining an end of cleaning of asemiconductor manufacturing apparatus having a semiconductor substrateprocess chamber, comprising the steps of:cleaning an interior of thechamber using plasma discharge etching; monitoring a temperature in thechamber using a temperature sensor; and detecting the end of cleaning bydetecting a transition in a rate of change of the monitored temperature.2. A method according to claim 1, wherein in the end of cleaning occursafter a predetermined period of time has elapsed from the occurrence ofthe transition in the temperature change rate, said predetermined periodof time resulting in overetching in the chamber.